1. Field of the Invention
The present invention relates to an X-ray computed tomography scanner, a data processing device, and a data processing method.
2. Description of the Related Art
As a scan method using an X-ray computed tomography scanner (hereinafter, referred to as “X-ray CT scanner”), a scan method of alternately repeating a circular orbital scan (conventional scan) and a movement of a top plate on which a sample is placed is known, for example, as disclosed in JP-A-2006-239303. By using this scan method, a very broad area can be scanned by a cone-beam (also referred to as “multi-slice”) CT. A circular orbital scan is a scan method of causing an X-ray tube to move in a circular orbit around a stationary sample.
The scanning process will be explained using the example of a triple pass circular orbital scan. First, the X-ray CT scanner performs a circular orbital scan on a first scan area of the sample, collects a projection data set from the first scan area, and reconstructs a volume data set from the first scan area on the basis of the collected projection data set. For example, the Feldkamp (FDK) reconstruction method is used as the reconstruction method. Then, the X-ray CT scanner moves the top plate relative to the X-ray tube and the X-ray detector to dispose the top plate at a second scan position. The X-ray CT scanner performs the circular orbital scan on a second scan area, collects a projection data set from the second scan area, and generates a volume data set from the second scan area. Then, the X-ray CT scanner moves the top plate relative to the X-ray tube and the X-ray detector to dispose the top plate at a third scan position. The X-ray CT scanner performs the circular orbital scan on a third scan area, collects a projection data set from the third scan area, and generates a volume data set from the third scan area.
However, the above-mentioned technique has the following problem. That is, even when the scan is performed under the same X-ray conditions, the CT value of the same anatomic site may be different during every scan for various reasons such as a scattered radiation distribution differences, radiation curing inside the sample caused by the X-rays, and an energy differences in the X-rays between cone-angle directions. As a result, the CT values in the boundary surface between the adjacent volume data sets may be discontinuous. Accordingly, differences in the CT values of the boundary surface between the adjacent volume data sets may result.